The present study is concerned with the effects of the chronic administration of blockers of dopamine and opiate receptors on developing dogs. The findings on the pimozide-treated animals were of particular interest, because in addition to the changes in the species-typical behavior and hypersensitive response to apomorphine described in last year's report, these animals were the only ones to show delayed estrus and failure in reproductive behavior. The neurochemical analysis has not yet been completed.